Various techniques of non invasive monitoring of conditions of a subject have been developed. These techniques include impedance-based measurement techniques, photoacoustic measurements, acoustic measurements (Doppler measurements), and optical measurements (e.g. oxymetry).
Another approach, based on use of ultrasound tagging of light in measurements of various chemical and physiological parameters, has been developed and disclosed for example in WO 06/097910 and WO 05/025399, both assigned to the assignee of the present application.